If $x \circledcirc y = x-3y$ and $x \bigtriangledown y = 3x+y$, find $4 \circledcirc (1 \bigtriangledown 0)$.
Explanation: First, find $1 \bigtriangledown 0$ $ 1 \bigtriangledown 0 = (3)(1)$ $ \hphantom{1 \bigtriangledown 0} = 3$ Now, find $4 \circledcirc 3$ $ 4 \circledcirc 3 = 4-(3)(3)$ $ \hphantom{4 \circledcirc 3} = -5$.